In conventional scanning apparatus, one approach has been to bolt various mountings for components onto the surface of an optical chassis. More importantly, we have recognized that the chassis used in the known scanning apparatus do not vibrationally and thermally isolate the chassis and its components from the remaining components in the housing, while at the same time, providing for prealignment of the optics so that the optical chassis with all the scanning apparatus (namely the gate, clamp, the gate drive system, the integrating cavity and the lens) can be preadjusted and interchanged with an existing optical chassis in a scanning apparatus.